Polystyrene and polyurethane forms are inexpensive materials to use as concrete forming devices, but such foam devices, due to their surface porosity and lack of structural integrity, can be quite difficult to remove in one piece from cured concrete.
It is known to provide liners for concrete forms, which liners are adapted for facilitated removal from cured concrete. For example, U.S. Pat. No. 3,844,527 to Scott, discloses a water permeable form liner for imparting a decorative pattern to poured concrete, this form liner also functioning to aid in the curing of concrete. These form liners are formed of integral skin foam or self skinning elastomeric plastic, such as polyurethane, the skin being of the same material as the rest of the form liner, and the skin facilitating the removal of the form liner from the hardened concrete. U.S. Pat. No. 4,017,051 to Scott et.al., discloses a smooth, rigid, non-stick plastic sheet liner for a concrete form which allows for simplified removal of the forms from the concrete, after the concrete sets. U.S. Pat. No. 3,350,049 to Reiland, illustrates bracing material for use in casting concrete columns and comprised of foamed plastic material such as foamed polystyrene or foamed polyurethane.
Attention is directed to the following U.S. patent documents, which relate to molds for forming concrete:
______________________________________ INVENTOR U.S. PAT. NO. ISSUED ______________________________________ Van Doren 4,181,236 January 1, 1980 Scott 4,037,816 July 26, 1977 Kreier, Jr. 3,317,178 May 2, 1967 Kreier, Jr. 3,295,818 January 3, 1967 ______________________________________